The invention relates to a device for trimming or cutting the top edges and/or the bottom edges of printed products. The printed products are arranged successively and spaced apart. The printed products rest on a flat side transverse to the conveying direction, preferably with the bound edge of the printed products conveyed forward. The printed products may be held by a conveying device of a conveyor. The printed products may be moved through a cutting tool that operates synchronized with the timing of the conveying device.
Devices of the aforementioned type may be used for cutting or trimming perfect-bound or wire-stitched printed products along three sides. Examples of such products include, but are not limited to, booklets, magazines, catalogs, paperback books, and/or other similar printed products. The cutting or trimming of the edges may represent a final operation to be carried out on the individual printed products, apart from inserting supplements, affixing addresses, stacking the products, or other similar tasks involving the finishing of the printed products. The appearance of the finished printed products may be significantly influenced by the quality of the trimming.
As a result of the characteristics of printed products, various configurations are known for the cutting tools or trimmers. These trimmers are also referred to as three-way cutters or automatic three-knife trimmers. A joint feature of known cutting devices may include conveying the printed products individually or in stacks in a serial flow through cutting devices, normally at a high clocking rate, and processing the printed products or trimming the printed products therein.
During the cutting or trimming, the printed products may be held while clamped and/or pressed between two essentially parallel bars, at least in the area directly adjacent to the cutting location. Cutting knives typically move in one plane and the blades typically form an acute angle with the flat sides of the printed products, at least at the start of the cutting operation. Such configuration may aid in the initial cut.
The cutting movement of the knives may be perpendicular to the flat sides of the printed products. However, superimposing a speed component parallel to the flat sides is also known, which results in a drawn-out cut. Counter knives or cutting bars for absorbing the cutting forces may be arranged on the sides of the printed products that are opposite the sides facing the knives. The top and bottom cuts may be generally made at the same time while the trimming of the front may be realized with a time offset, meaning the front trimming occurs either before or after the trimming of the top and bottom.
European patent document EP 0 698 451 B1, for example, discloses a device of the aforementioned type. The printed products are conveyed with a constant speed and with the aid of grippers, attached uniformly spaced apart to a circulating traction device. The printed products are conveyed through the cutting device and are trimmed during the conveying operation with the aid of cutting or trimming units, which in part also move along.
Also known are devices in which the printed products are cyclically accelerated and delayed. These devices trim printed products by locally fixed trimming units while the printed products are stopped. The cutting edges of the knives extend nearly parallel to the flat sides of the printed products while the knives move perpendicular to the flat sides. However, considerable stresses can occur in the printed products during the trimming operation. Such stresses can be high enough to damage and/or tear the covers on the back, in the areas adjacent to the trimming.
Swiss patent document CH 565 632 proposes that a specific portion of the cutting edge of the side knives, which is used for cutting the back of the booklet during the top and bottom trimming, encloses an angle of between 60° and 90° with the plane upon which the booklet rests. The embodiment shown in FIG. 1 of the Swiss patent document shows that damage to the back area of the cover can be avoided. However, a disadvantage of this device is that uneven cutting surfaces may result due to the simultaneous cutting from two outer regions of the printed products. With the embodiment according to FIG. 3 of the Swiss document, the angle α′ must be nearly 90° because one component of the cutting force is directed away from the back. Therefore, a large knife stroke is required perpendicular to the resting surface and/or the flat side of the printed product.
German patent document DE 103 25 378 A1 proposes that the trimming knife has a knife edge composed of a first section and a second section. The second section is positioned at an angle relative to the first section. A disadvantage of this device, however, is that a larger knife stroke is required perpendicular to the flat sides of the printed products.
According to the method proposed in European patent document EP 1 410 925 A2, the printed products are configured so that the book back encloses an acute angle with the resting surface and that one component of the cutting forces is directed toward the back. However, a disadvantage of this method is that the strong deformation of the printed products may result in excessive stress to the binding and/or that the back of the printed product may experience a permanent deformation.
The German patent document DE 103 57 815 A1 proposes a pre-scoring of the cutting region on the back of the printed product, using a laser beam. A disadvantage of this method is that the burning of the cover surface causes dangerous smoke to develop, which may endanger health and must be suctioned off. In addition, a system with the capacity required for realizing this method is extremely involved, expensive, and difficult to regulate. Measures must also be taken to prevent danger to the personnel caused by the laser, as well as precautions to prevent fire.